EFFECTS OF A MULTIFUNCTIONAL ADDITIVE ON BOUND RUBBER IN CARBON-BLACKAND SILICA FILLED NATURAL RUBBERS

The effects of a multifunctional additive (MFA), i.e. a diamine salt o f a carboxylic acid, on the bound rubber in carbon black and silica fi lled natural rubber compounds in o-xylene, have been studied. For the carbon black filled compound, the bound rubber initially decreases wit h the MFA concentration and then does not change significantly above a n MFA concentration which approximately corresponds to the monolayer s urface coverage of the carbon black. This phenomenon has been explaine d in terms of the release of immobilised rubber within the carbon blac k agglomerates. Bound rubber measured at high temperatures indicated t hat the MFA did not improve the chemical interaction between the carbo n black and the rubber in an unvulcanised rubber mix. The MFA has no p ronounced effects on the bound rubber for silica. This may be caused b y the combined effects of improved filler dispersion and silica-rubber interfacial interaction. The ozone oxidation of the carbon black sign ificantly increases its surface oxygen concentration but has little ef fect on its specific surface area. The oxidation has been found to dec rease the bound rubber.